1. Field of the Invention
This invention relates to a platinum (IV) complex having excellent therapeutic effects on malignant tumors and to a pharmaceutical composition comprising the platinum (IV) complex.
2. Discussion of the Background
In recent years, malignant tumors became the top of the cause of death, and various anti-malignant tumor drugs have been developed to treat them. As a platinum complex among these drugs, a cisplatin has already been used. However, the cisplatin sometimes causes serious nephropathy as a side effect, so that its use must often be limited. In addition, since the cisplatin is slightly soluble in water and organic solvents, the route of administration is also limited. In consequence, a carboplatin (Saishin Igaku, 41(3):509 (1986)) has been developed and marketed as a derivative of the cisplatin having a reduced renal toxicity and an increased solubility in water. Also, in recent years, in addition to divalent platinum complexes including the cisplatin and the carboplatin as representative examples, tetravalent platinum complexes, typically an iproplatin (a compound disclosed in JP-A-57-77694; the term "JP-A" as used herein means an "unexamined published Japanese patent application"), have been developed. Their antitumor effects have been shown, for example, in JP-A-61-33192, JP-A-61-7283, JP-A-62-207283, JP-A-1-294684, JP-A-2-4797, JP-A-2-96523, JP-A-8-20594, JP-A-8-27174 and JP-A-8-259581. These tetravalent platinum complexes have characteristics in that they have excellent water solubility and low renal toxicity. Some of them have a high lipophilicity and can be orally administered. However, their antitumor effects are not always satisfactory.